With continuing demand of the industry, deposition of films with increased growth rate meaning increased throughput in high-volume manufacturing is desirable. Traditional ALD is a self-limiting process, whereby alternated pulses of reaction precursors saturate a substrate surface and leave no more than one monolayer of material per pulse. The deposition conditions and precursors are selected to ensure self-saturating reactions, such that an adsorbed layer in one pulse leaves a surface termination that is non-reactive with the additional gas phase reactants of the same pulse. A subsequent pulse of different reactants reacts with the previous termination to enable continued deposition. Thus each cycle of alternated pulses leaves no more than about one molecular layer of the desired material. The principles of ALD type processes have been presented by T. Suntola, e.g. in the Handbook of Crystal Growth 3, Thin Films and Epitaxy, Part B: Growth Mechanisms and Dynamics, Chapter 14, Atomic Layer Epitaxy, pp. 601-663, Elsevier Science B.V. 1994, the disclosure of which is incorporated herein by reference.
As described herein, Atomic Layer Deposition (ALD) processes can be used to deposit thin films comprising pnictogens and chalcogenides, wherein some of those materials contain Antimony (Sb) and Tellurium (Te). Such thin films can be related to phase change materials and used for phase change memory (PCM) technology. Deposition of Te or (Selenium) Se containing films by ALD or group VA element, e.g. pnictide, films by ALD are described, for example, in U.S. Patent Application No. 20100009078 and U.S. Patent Application No. 20090324821 and International Patent Application Publication WO2011/056519 (PCT application No. PCT/US/2010/053982), the disclosures of which all are incorporated herein by reference in their entirety.
As described herein, VA elements refer to group VA under the American, Chemical Abstract Service (CAS), system which is synonymous with Group 15 under the new International Union of Pure and Applied Chemistry (IUPAC) system and VB under the old IUPAC system. VA elements as referred to herein are also known as the pnictogens or nitrogen family and includes nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb) and bismuth (Bi). Thin films comprising group VA elements, Te, Se or a combination thereof are used in many different applications, including, for example, non-volatile phase-change memories (PCM), solar cells, III-V compounds and optical storage materials. III-V compound semiconductors can be used in many different application areas, including transistors, optoelectronics and other application areas, for example, in bipolar transistors, field effect transistors, lasers, IR detectors, LEDs, wide band gap semiconductors, quantum well or quantum dot structures, solar cells and in monolithic microwave integrated circuits.
The operation of PCM cells is based on the resistivity difference between amorphous and crystalline states of the active material. A resistivity difference of more than three orders of magnitude can be obtained by many different phase change alloys. The switching in a PCM cell is generally accomplished by heating the material locally with suitable current pulses, which, depending on the intensity of the pulse, leave the material in a crystalline or amorphous state.
A wide variety of different PCM cell structures have been reported, many of which use trench or pore-like structures. Sputtering has typically been used in preparing PCM materials, but the more demanding cell structures will require better conformality and more control of the deposition process. Sputtering may be capable of forming simple pore and trench structures, however, more advanced PCM applications require more complicated 3-D cell structures that cannot be formed using sputtering techniques. Processes with greater precision and control, such as atomic layer deposition (ALD), are required to make these complicated structures. Using an atomic layer deposition process provides greater precision and control over the deposition, including better conformality and better control of the composition of the deposited film.
For PCM technology to compete with other memory technologies it is desirable to increase the throughput of the growth process of the PCM materials to decrease the cost associated per memory unit.
A need exists, therefore, for methods to increase the growth rate of an ALD process of the above mentioned materials including materials comprising group VA elements, Te, Se or a combination thereof.